Offset Rotor Sections Reduce Torque Ripple in IPM Motors
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Solution Overview
Problem
Current electric machines, such as interior permanent magnet (IPM) and Synchronous Reluctance motors, face manufacturing challenges and torque ripple issues that lead to damage and inefficiency, particularly in applications requiring high torque at low speeds, like underground mining vehicles, due to the insertion of permanent magnets and torque oscillations.
Innovation Solution
The design incorporates a step-skewed rotor structure with multiple axial sections and keybars on a longitudinal axle, allowing for easier magnet insertion and reducing torque ripple by angularly shifting rotor sections, which decreases the amplitude of torque oscillations and simplifies manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If permanent magnets are inserted entirely through the rotor slot depth to fill the entire stack length, then the magnetic field strength is improved, but the manufacturing complexity and risk of damage to magnets and laminations increases
Solution Approach 1:
The rotor is divided into multiple discrete rotor sections along the axial direction, each with its own magnets. This segmentation allows magnets to be inserted into individual sections rather than through the entire rotor stack length, reducing insertion force requirements and manufacturing complexity while maintaining overall magnetic field strength through the combination of multiple sections.
2Reliability
If continuous stator skewing is applied to reduce torque ripple, then torque oscillations are reduced, but manufacturing cost and complexity increase due to additional coil insertion complexity
Solution Approach 1:
Instead of continuous stator skewing, the invention uses discrete rotor sections that are axially offset from each other. This segmentation approach achieves torque ripple reduction through the distributed magnetic fields of offset sections without requiring complex skewed stator coil windings, thereby reducing manufacturing complexity while maintaining reliability benefits.
Solution Approach 2:
The invention transitions from skewing in the circumferential direction (stator skewing) to offsetting in the axial dimension (rotor section positioning). This dimensional change achieves torque ripple reduction through axial displacement of rotor sections rather than circumferential skewing, simplifying manufacturing while maintaining effectiveness.
3Reliability
If an odd number of stator slots per pole pair is used to reduce torque ripple, then torque oscillations are reduced, but core losses increase which harms efficiency
Solution Approach 1:
The use of multiple discrete rotor sections with axial offsets provides an alternative mechanism for torque ripple reduction that does not rely on the odd-numbered stator slot configuration. This allows the use of conventional even-numbered slot arrangements, maintaining lower core losses while achieving torque ripple reduction through the segmented rotor structure.
4Force
If high torque at low speeds is required for underground mining vehicles, then the motor meets application requirements, but torque ripple may cause damage to the rotor and gearbox
Solution Approach 1:
Multiple rotor sections with axial offsets distribute the torque generation across separate magnetic fields that do not peak simultaneously. This segmentation smooths the total torque output by averaging the ripple from individual sections, reducing peak torque variations that could damage mechanical components while maintaining high average torque output for mining vehicle applications.
Data Source
AI summary
A motor rotor assembly that includes multiple motor rotor sections and a rotor bar that extends through the motor rotor sections, such that the rotor bar and the motor rotor sections are configured such that the rotor sections are step-skewed, or continuously skewed, from each other. The assembly may be used in an IPM or Synchronous Reluctance motor; and, the motor rotor sections may be of solid core or laminations. Various assembly components, IPM and Synchronous Reluctance motors, and methods of construction/assembly are also disclosed. The present invention has been described in terms of specific embodiment(s), and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.